Direct alpha spectrometry with three different filter types was investigated for the determination of thorium air concentrations at workplaces in the manufacturing process of discharge lamps containing thoriated tungsten electrodes.

The method was compared with neutron activation analysis over an activity range of five orders of magnitude.

Within the experimental limits of error, both methods were found to be comparable with respect to sensitivity and accuracy.

The advantage of direct alpha spectrometry, however, is that it is less laborious than neutron activation analysis and that it supplies information on the degree of radioactive equilibrium of the thorium series, which is important with regard to the estimation of dose.